This invention relates to a magnetoresistance effect (MR) element, its manufacturing method, magnetic recording element and magnetic memory. More particularly, the invention relates to a magnetoresistance effect element having magnetic nanocontacts that exhibit high magnetoresistance ratios, its manufacturing method, magnetic reproducing element and magnetic memory.
Since the discovery that giant magnetoresistance effect is expressed when a current is supplied to flow in parallel with the major plane of a multi-layered structure, efforts have been paid to find systems having still larger magnetoresistance ratios. Heretofore, ferromagnetic tunnel junction elements and CPP (current perpendicular to plane) type MR elements in which electric current flows vertically in a multi-layered structure have been developed and regarded hopeful as magnetic sensors and reproducing elements of for magnetic recording.
In the technical field of magnetic recording, enhancement of the recording density inevitably requires miniaturization of the recording bit, and this makes it more and more difficult to ensure sufficient signal intensity. Accordingly, materials exhibiting more sensitive magnetoresistance effect are demanded, and the importance of systems having large magnetoresistance ratios as referred to above is getting higher and higher.
Recently, “magnetic nanocontacts” by tip-to-tip abutment of two nickel (Ni) needles and nanocontacts by contact of two magnetite elements were reported as elements exhibiting 100% or higher magnetoresistive effects in the literatures, (1) Garcia, M. Munoz and Y.-W. Zhao, Physical Review Letters, vol. 82, p 2923(1999) and (2) J. J. Versluijs, M. A. Bari and J. W. D. Coery, Physical Review Letters, vol. 87, p 26601-1 (2001), respectively. These nanocontacts certainly exhibit large magnetoresistive changes. In both proposals, however, the magnetic nanocontacts are made by bringing two needle-shaped or triangular-shaped ferromagnetic elements into tip-to-tip contact.
More recently, magnetic nanocontacts which was formed by arranging two thin nickel wires in a “T”-configuration and by growing a micro column at the connecting point thereof by electroplating technique were reported in the literatures, (3) N. Garcia et. al., Appl. Phys. Lett., vol. 80, p 1785 (2002) and (4) H. D. Chopra and S. Z. Hua, Phys. Rev. B, vol. 66, p. 20403-1 (2002).
These magnetic nanocontacts exhibit a large mangetoresistance change, however, the structure of the nanocontacts makes it almost impossible to realize a practical magnetoresistance effect element.
Another group has reported a magnetic nanocontact which was formed by growing a cluster of nickel by an electroplating technique in a pinthrough hole made on an alumina layer in the literature, (5) M. Muñoz, G. G. Qian, N. Karar, H. Cheng, I. G. Saveliev, N. García, T. P. Moffat, P. J. Chen, L. Gan, and W. F. Egelhoff, Jr., Appl. Phys. Lett., vol. 79, p. 2946, (2001).
However, it is difficult to control the magnetic domain structure and the configuration of the point contact, therefore, the resulted magnetoresistance ratio is as small as 14% or even smaller.
Magnetic nanocontacts have a potential to exhibit a large magnetoresistance ratio, however, in order to ensure a large magnetoresistive effect therewith, structures proposed by those literatures must put two needle-shaped ferromagnetic elements in tip-to-tip abutment ensure or they must grow a micro column between two wires by an electroplating technique, and this and other requirements make it difficult to accurately control the contact portions in the manufacturing process. Taking account of their application to magnetic heads or solid magnetic memory devices, it is necessary to develop a structure of nanocontacts suitable for mass production under reasonable control, as well as its manufacturing method. Additionally, to detect the difference in magnetization directions of opposite sides of a nanocontact, control of magnetic domains of both magnetic electrodes is important. Therefore, in order to realize a practical magnetoresistance effect element, it is essential to develop a structure where the control of the magnetic domains of the both magnetic electrodes is quite easy.